In situ microscope FTIRS studies of CO adsorption on an individually addressable array of nanostructured Pt microelectrodes - an approach of combinatorial analysis of anomalous IR properties

Combinatorial spectroelectrochemical analysis was carried out in the present paper by combining in situ microscope FTIR spectroscopy with an individually addressable array of Pt microelectrodes (MEij). A series of nanostructured films was created on the array through a treatment of fast potential cycling with varying duration (tau). STM studies illustrate that a nanostructured film is composed of Pt islands. The film thickness and island size increase consecutively on MEij of the array along with the increasing duration tau. Using CO adsorption as the probe reaction, anomalous IR properties of nanostructured films on the array were investigated systematically. It was revealed that anomalous IR properties depended strongly on the nanostructure of Pt thin films on the array. Following the increase of the film thickness and the size of Pt islands on the film, the IR features of CO linearly adsorbed (COL) on Pt microelectrodes of the array underwent the following various changes: (1) the spectral line shape of IR absorption of the COL species was changed from the negative-going monopolar band (normal IR absorption) to the bipolar band, and finally to the positive-going monopolar band; (2) the center of the COL band presented a volcano-type variation; that is, the positive-going COL band center ((v) over tilde (COL(I))) increased progressively from 2076 cm(-1) to a maximum 2082 cm(-1), then decreased to 2070 cm(-1); (3) the stark tuning rate (d (v) over tilde (co)/dE) of the COL band was decreased gradually; (4) the full width at half-maximum (fwhm) of the COL band reached the maximum at tau = 100 min but, thereafter, decreased gradually; and (5) the enhancement of IR absorption of COL species was determined to yield the maximum 6.73 at tau = 100 min. Besides the anomalous IR properties, the electrocatalytic activity of the array for CO oxidation was also studied by cyclic voltammetry. The present study has shed light on the intrinsic relationship between nanostructures of Pt film materials and anomalous IR properties as well as their electrocatalytic activity.